A National Association of Realtors index tracking pending sales of existing homes increased 4.3 percent in August but fell 20.1 percent compared to the same month last year, the trade group announced today.

NAR’s latest economic forecast, also released today, anticipates a 6.4 percent drop in existing-home sales this year compared to 2009, to 4.82 million, with the median price of existing homes up 0.2 percent, to $172,900.

NAR forecasts existing-home sales to rise 7.1 percent in 2011 and 4.3 percent in 2012, with the median price up 0.5 percent in 2011 and 2.3 percent in 2012.